This invention relates to a bottom unheading device for vertical vessels, such as coking drums which are adapted for remote operation. It particularly relates to such a bottom unheading device for removing and replacing a lower cover unit for coking drums and to a method for remote operation of the unheading device.
During the operation of delayed coking drums or vessels for coking various heavy hydrocarbon materials in petroleum refinery operations, the resulting coke is deposited progressively on the inner walls of the drum and when full must be removed, usually at 36-48 hour intervals. A typical decoking apparatus for such coking drums is disclosed by U.S. Pat. No. 4,611,613 to Kaplan. Such coke removal from coking drums is accomplished through an opening in the lower end of the vertically-oriented drum, and is usually accomplished by manually removing a lower flange cover and installing a chute to direct the coke removed to a desired location, such as to a hopper or rail car. Because the coking drum operates at relatively high temperatures of 800.degree.-900.degree. F., such removal of the hot coking drum lower cover by manual means is slow and hazardous and is therefore undesirable.
A useful remotely operated unheading device for coking drums is disclosed by U.S. Pat. No. 4,726,109 to Malsbury et al now U.S. Pat. No. 4,726,109. However, this prior unheading device has been found to have some basic deficiencies, which have been overcome by this invention. Accordingly, the invention advantageously provides an improved bottom unheading device for vertical vessels such as coking drums for remote safe and reliable removal and replacement of a coking drum lower cover unit, and enables more convenient and rapid removal of coke from the drum during decoking operations.